Method for producing gallium



United States Patent C 3,325,383 METHOD FGR PRODUCENG GALLIUM Georg lwantscheff and Richard Dotzer, Number-g, Germany, assignors to Siemens-Elchuchertwerke Alrtiengeseliscliaft, Berlin-Siemensstadt, Germany, a corporation of Germany No Drawing. Filed May 5, 1964, Ser. No. 365,155 Claims priority, application Germany, 9, 1960,

The portion of the term of the patent subsequent to Jan. 26, 1982, has been disclaimed 2 Claims. (Cl. 2'04--105) The instant application is a continuation-in-part of our applications 93,865, filed Mar. 7, 1961, now abandoned, and 102,386, filed Apr. 12, 1961, now U.S. Patent No. 3,167,422.

Our invention relates to the production of gallium and has as an object an improved process for producing gallium considerably more economical than previously possible.

We produce gallium by separating it from certain anode slimes occurring during electrolysis.

In electrorefining of metals, the impure metal is made the anode in a solution or a molten salt of the metal being refined. The pure metal deposits at the cathode during electrolysis. The so-called anode slimes occurring at the anode are of no significance to the recovery of the refined material deposited at the cathode. These anode slimes, however, often contain nobler metals in quantities sufficient to Warrant further rocessing for their recovery. Thus, it is known that large-scale industrial electrorefining of copper may only become profitable by recovering the gold and silver content of the anode slimes.

It has been found that the anode slime occurring in the electrorefining of certain metals in organometallic complex salts or in their solutions, contains a number of elements in concentrations that economically justify recovery. These slimes contain the transition metals Ag, Cr, Cu, Fe, Mn, Mo, Ni, Ti and V which accumulate in the anode slime, as can be expected on the basis of their organometallic chemical behavior. It has also been discovered that these slimes, aside from the elements Pb, Si, Sn and Zn, contain the elements Ga and In, despite the fact that the latter two elements are capable of forming fugitive metal alkyls. It is known that the anodic dissolution of the aluminum is produced by alkyl radicals electrochemically liberated from the electrolyte by formation of Al-trialkyl (see K. Ziegler and H. Lehmkuhl, Zeitschrift fiir anorganische und allgemeine Chemie, volume 283, 1956, pages 414-424). The discovery of substantial quantities of Ga and In in the slime is surprising as, individually, these elements can be dissolved in the same electrolyte when used as anodes.

According to our invention, the above-mentioned discovery is utilized in providing an improved process for the production of gallium at lower cost than theretofore possible. We produce gallium by processing the anode slimes which occur in the electrorefining of metals or the anodic dissolution of metals in organometallic complex salt melts or in solutions of these organometallic complex salts.

The technological importance of this method according to the invention becomes apparent when one considers that heretofore gallium was produced by a relatively complicated method from aluminum waste liquors (the socalled Bayer process waste liquors) which have a gallium concentration for example of 70 g./t. (gram per metric ton), whereas the anode slimes to be used according to the invention exhibit gallium enrichments up to about 1000 g./t.

Gallium is produced according to the invention from anode slimes that result in the electrolysis of metals in molten baths of complex salts of the formula and in solutions of the above salts in aromatic hydrocarbons, e.g. benzene (benzol) and toluene (toluol). In the above formula, Me denotes an alkali metal or a quaternary ammonium, R an alkyl, R an alkyl or halogen or hydrogen and x the numeral one (1) or two (2).

Gallium can also be produced from slimes that occur in the anodic dissolution of aluminum alloys, lead, gallium, indium, and other elements of the second, third, fourth and fifth groups of the periodic system of elements in the above-mentioned electrolyte systems. The anode slimes resulting in the electrorefining of gallium and indium in organogallium and organoindium melts of complex salts and their solutions in aromatic hydrocarbons are also applicable.

The production method of the invention is particularly important in view of the fact that although the other elements in the residue can be economically produced by other methods and means, the instant invention presents a method of producing gallium more economically than heretofore known. Gallium constitutes an essential constituent in electronic semiconductor substances as Well as a doping agent in the production of other semiconductor materials of extrinsic conductance.

The gallium can be separated from the anode slime by any suitable and known physical or chemical method. Examples of physical separating techniques are:

Utilization of density differences in liquids and in gases, e.g. eddy-layer methods, centrifugal extraction, evaporation, sublimation, and distillation.

Also applicable are chemical methods for separating the gallium from the slime. Examples of such methods are:

Separation by partial oxidation, amalgamating and/ or alloy formation, electrochemical process and partial dissolving reactions.

Of particular interest are the reactions of the gallium with halogens and halogen hydrides. For example, the gallium contained in the anode slime is converted to a gallium halide and then dissolved in hydrocarbon solvents, as pentane and/ or hexane and/ or heptane, leaving in the slime the corresponding halides of aluminum and indium. Thereafter, the gallium can be recovered from the solution in known manner for example by electrolytic processing. This method advantageously utilizes the discovered relatively high solubility of the gallium halides, as compared to the corresponding halides of aluminum and indium.

Moreover, physical and chemical methods for separating gallium from the anode slime can be combined. One or more of the above-mentioned physical methods can be combined with one or more of the above-mentioned chemical methods.

For storing and transporting the residues, it is preferable to humidity or cover these residues with alkylhalides and/or Al-alkyls (Al-triisobutyl and/or Al-triethyl).

The slimes step together during and after electrolysis with the aid of a diaphragm such as asbestos, woven cotton web, hard paper, clay, glass Wool, glass-sinter substance, cork, porous polyethylene, porous epoxy resin and/or porous polypropylene and the like. The following example is to illustrate, but not to limit, the present invention:

Example Anode slime, resulting from aluminum electrorefining in the electrolyte system NaF-2Al(C H sodium fluoride diialuminum hexaethyl, was held together in a cotton diaphragm. The electrolyte complex salt was washed away with benzene with exclusion of air and humidity and subsequently dried under reduced pressure. A finely distributed black powder was obtained. The following elements, other than aluminum, were analyzed in the powder (approximate numerical values in ppm):

Ag 100 Co 50 Cu 10,000 Cr 200 Fe 100,000 Ga 1,000 In 1,000 Mg 300 Mn 3,000 Mo 800 Ni 1,000 Pb 4,000 Sn 250 Ti 1,000 V 800 Zn 15,000 Zr 2,000

Because of the high reduction potential of molten and liquid aluminum, the above-listed elements are present in metallic form, whereby further processing for gallium recovery is greatly facilitated. The finely distributed powder is slowly heated in a current Olf HCl which, at first, is diluted with nitrogen. The heating is continued until a strongly exothermic reaction commences. This reaction converts the main constituent aluminum (about 80%) together with Fe, Ga, In, Mn, Sn, Ti, V, Zn and Cr into chlorides. Upon completion of the reaction, aluminum chloride together with the fugitive chlorides of gallium and indium is Sublimated at temperatures between 300 and 600 C. in a HCl current. The sublimate is treated with boiling n-hexane. Due to the above-mentioned discovery of the high preferential solubility of gallium chloride, one liter of saturated solution at 60 C. contains 1.35 g. of AlCl 1230 g. GaCl and only 0.17 g. InCl This makes it a simple process to separate GaCl from the AlCl and InCl and to obtain gallium chloride in solid form after distilling off the solvent. The GaCl can then be processed to obtain gallium in any known manner, e.g. by electrolysis of an alkaline solution.

In the above-mentioned processing of the metal halide, n-hexane can be substituted by other hydrocarbons such as pentane, heptane, cyclohexane or methyl cyclohexane.

The process according to the foregoing example can be similarly performed if one uses as starting product a slime resulting from the anodic dissolution of one or more of the elements from the second, third, fourth and fifth groups of the periodic system.

In the process according to the foregoing example equal All KP 2A1 (i-C H 3 We claim:

1. The method of producing gallium, which comprises separating gallium from the anode slime resulting from electrolysis of a gallium-containing metal in an organometallic complex salt of the formula MeR-xAlR(R') wherein Me is selected from the group consisting of the alkali metals and quaternary ammonium, R is an alkyl, R is selected from the group consisting of alkyl, hydrogen and halogen and x is an integral number selected from 1 and 2, by converting the gallium contained in the anode slime into a gallium chloride, dissolving said chloride in a hydrocarbon selected from the group consisting of pentane, hexane, heptane, cyclohexane, methyl cyclohexane and mixtures thereof, whereby the gallium chloride is concentrated and then recovering the gallium from the solution.

2. The method of producing gallium, which comprises separating gallium from the anode slime resulting from the electrolysis of a gallium containing metal in sodium fluoride dialuminum hexaethyl [NaF-2Al(C H by heating said anode slime in an HCl current to convert the elements in said slime to their respective chlorides, dissolving said chloride in a hydrocarbon selected from the group consisting of pentane, hexane, heptane, cyclohexane, methyl cyclohexane and mixtures thereof whereby the gallium chloride is concentrated, distilling off the solvent and recovering gallium from the solution.

References Cited UNITED STATES PATENTS 2,598,777 6/1952 Frary 20464 X 2,823,096 2/1958 Frevel et al. 23-l6 2,848,398 8/1958 Inagaki 204l05 2,849,349 8/1958 Ziegler et al. 20459 3,075,901 1/1963 Hutter et al. 204l05 3,167,422 1/1965 Iwantscheff et al. 7584.5

JOHN H. MACK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

H. S. WILLIAMS, Assistant Examiner. 

1. THE METHOD OF PRODUCING GALLIUM, WHICH COMPRISES SEPARATING GALLIUM FROM THE ANODE SLIME RESULTING FROM ELECTROLYSIS OF A GALLIUM-CONTAINING METAL IN AN ORGANOMETALLIC COMPLEX SALT OF THE FORMULA MER''$XALR(R'')2, WHEREIN ME IS SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METALS AND QUATERNARY AMMONIUM, R S AN ALKYL, R'' IS SELECTED FROM THE GROUP CONSISTING OF ALKYL, HYDROGEN AND HALOGEN AND X IS AN INTEGRAL NUMBER SELECTED FROM 1 AND 2, BY CONVERTING THE GALLIUM CONTAINED IN THE ANODE SLIME INTO A GALLIUM CHLORIDE, DISSOLVING SAID CHLORIDE IN A HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF PENTANE, HEXANE, HEPTANE, CYCLOHEXANE, METHYL CYCLOHEXANE AND MIXTURES THEREOF, WHEREBY THE GALLIUM CHLORIDE IS CONCENTRATED AND THEN RECOVERING THE GALLIUM FROM THE SOLUTION. 